The present invention relates to an improved mooring system, and to an offset anchoring system for anchoring an object to a sea bed floor and which can be used in conjunction with the improved mooring system.
Conventional moorings comprise a base which is fixed to the sea bed, and a length of chain or the like fixed at one end to the base and fixed at the other end to a mooring line supported from the surface of the water by a buoy. A mooring line of a vessel may be attached to the buoy when mooring the vessel. When a vessel is attached to the buoy, the base and chain serve to prevent movement of the vessel away from the mooring. The function of the chain is to absorb the inertial load created by the movement of the vessel away from the mooring as a result of water conditions by providing a reaction to the forces applied by the vessel. As the load applied by the vessel increases, so more of the chain will be lifted from the sea bed. When maximum load has been applied by the vessel, the chain is lifted free of the sea bed and the load of the chain is fully applied to the base.
A disadvantage of the above-described arrangement is the amount of space that must be provided between moorings in order to allow the free movement of a vessel under extreme water conditions. A further disadvantage of such prior art moorings is that as the vessel swings about the mooring, due to changing wind, tidal and wave conditions, the chain is dragged over the sea bed around the mooring. This results in erosion of the sea bed around the mooring base, and damages any sea grass, coral and other marine life that may be growing in the region surrounding the mooring base.
Australian Patent No. 688397 describes a mooring means having a sheave adapted to be mounted to a base which is located on the sea bed. A cable received in the sheave has one end adapted to be connected to the mooring line of a vessel and the other end is connected to a first buoy. A second buoy is attached to the cable between the sheave and the one end. The second buoy has a buoyancy less than that of the first buoy and is positioned on the cable such that under a no load condition it is submerged and lies adjacent the cable between the sheave and first buoy. The buoyancy of the first buoy is sufficient to accommodate the anticipated loading of the mooring. A counteracting tension is provided by the second buoy against the first buoy which serves to retain all of the pendant assembly of the mooring line above the sea bed floor. As a result, damage to the sea bed floor is minimised with this system. However, in practice over extended periods, it was found that the sheave becomes encrusted with debris and the cable is no longer free to run through the sheave.
The present invention was developed with a view to providing an improved mooring system that is less susceptible to the problems encountered in the pnor art.
For the purposes of this specification it will be clearly understood that the word “comprising” means “including but not limited to”, and that the word “comprises” has a corresponding meaning. Throughout this specification the term “sea bed” should be taken to include the bottom of any large body of water, including a river bed or lake bed.